The invention relates generally to optical switches and more particularly to an optical switch having micromachine-actuated mirrors.
Continuing innovations in the field of fiber optic technology have contributed to the increasing number of applications of optical fibers in different technologies. With the increased utilization of optical fibers, there is a need for efficient peripheral devices that assist in the transmission of data through these optical fibers, such as optical switches. An optical switch operates to selectively couple an optical fiber to one of two or more alternative optical fibers such that the two coupled optical fibers are in communication with each other.
The coupling of the optical fibers performed by an optical switch can be effectuated through various methods. One method of interest includes using a mirror that is placed in front of an input optical fiber to reflect optical signals from the input optical fiber to at least one of two output optical fibers. The input and output optical fibers may be either uni-directional or bi-directional fibers. In the simplest implementation of the mirror method, the input optical fiber is aligned with one of two output optical fibers, such that when the mirror is not placed in an optical path between these two aligned optical fibers, the two aligned optical fibers are in a communicating state. However, when the mirror is placed between the two aligned optical fibers, the mirror steers, i.e., reflects, optical signals from the input optical fiber to the other output optical fiber. The positioning of the mirror in and out of the optical path between the two aligned optical fibers can be accomplished by using an apparatus that mechanically moves the mirror to a desired position.
U.S. Pat. No. 5,208,880 to Riza et al. describes an optical switch that utilizes a piezoelectric actuator to displace a mirror to selectively couple an input optical fiber to a particular output optical signal. The piezo-electric actuator of Riza et al. includes a number of piezoelectric bars, also known as unimorphs, to linearly displace the mirror. In a first embodiment, the optical switch of Riza et al. includes N output optical fibers that are positioned perpendicularly to an input optical fiber in a side-by-side configuration. The mirror is positioned on the axis of the input optical fiber and has a reflective surface that is orientated to direct optical signals from the input optical fiber at a right angle. The mirror is coupled to the piezoelectric actuator that is able to displace the mirror along the axis of the input optical fiber to couple the input optical fiber to any one of the output optical fibers. In operation, the piezoelectric actuator linearly displaces the mirror to a location where the axis of the input optical fiber intersects an axis of a preselected output optical fiber. The mirror at the intersecting location reflects optical signals from the input optical to the preselected output optical fiber and reflects optical signals from the preselected output optical fiber to the input optical fiber. The input optical fiber can be optically coupled to another output optical fiber by linearly displacing the mirror to a new location, where the axis of the input optical fiber intersects an axis of the to-be-coupled output optical fiber.
In a second embodiment, the optical switch of Riza et al. is configured to accommodate two input optical fibers and two output optical fibers. The optical fibers are positioned in an xe2x80x9cXxe2x80x9d configuration such that two output optical fibers are located in the upper portion of the configuration and the two input optical fibers are located in the lower portion of the configuration. In this embodiment, the optical switch of Riza et al. includes a thin mirror that has reflective surfaces on both sides. The mirror can be positioned in the optical paths between the optical fibers by the piezoelectric actuator such that when the mirror is displaced to the center of the xe2x80x9cXxe2x80x9d configuration, the lower left optical fiber is coupled to the upper left optical fiber and the lower right optical fiber is coupled to the upper right optical fiber (the xe2x80x9creflective statexe2x80x9d). However, when the mirror is removed from the optical paths, the lower left optical fiber is coupled to the upper right optical fiber and the lower right optical fiber is coupled to the upper left optical fiber (the xe2x80x9cpassive statexe2x80x9d).
U.S. Pat. No. 5,042,889 to Benzoni describes an optical switch that also uses a mirror to switch optical paths between optical fibers. In an exemplary embodiment, the optical switch of Benzoni is configured to accommodate four optical fibers that are positioned in the above-described xe2x80x9cXxe2x80x9d configuration. In contrast to the optical switch of Riza et al., the optical switch of Benzoni utilizes an electromagnetic mechanism, instead of a piezoelectric actuator, to move the mirror in and out of the optical paths between the optical fibers. The electromagnetic mechanism operates to create an attractive magnetic force between the mechanism and the mirror. The upper section of the mirror includes a ferromagnetic material that becomes attracted to the electromagnetic mechanism when the magnetic force is generated. The electromagnetic mechanism is located above the mirror to lift the mirror when the mechanism is activated. Initially, the mirror is positioned between the optical paths such that the four optical fibers are coupled in the reflective state. When the electromagnetic mechanism is activated, the attractive magnetic force causes the mirror to be lifted out of the optical paths to set the optical fibers in the passive state.
Although the known optical switches operate well for their intended purpose, what is needed is an optical switch that includes a compact actuator to precisely position an associated mirror using low operating voltage, so that the actuator is compatible with complementary metal-oxide semiconductor (CMOS) circuitry.
An optical switch uses a surface electrostatic actuator to mechanically pivot a reflector about a pivot region that is substantially parallel to the drive surfaces of the actuator. The pivoting reflector selectively redirects an optical beam. In one application, the electrostatic actuator and the reflector form a switching device to redirect optical signals between two optical fibers such that the two optical fibers are in communication.
The optical coupling of the optical fibers is accomplished by pivoting the reflector from a non-reflective orientation to a reflective orientation. The non-reflective orientation is the position of the reflector in which the reflecting surface of the reflector is generally parallel to the upper surface of a first member, which may be stationary (i.e., a stator). When the reflector is in the non-reflective orientation, any optical signal that propagates through the switch is allowed to continue propagation in the original direction. The reflective orientation is the position of the reflector in which the reflecting surface is perpendicular to the upper surface of the first member. In this orientation, the reflector redirects any optical signal that propagates through the switch, thereby optically coupling two optical fibers that have axes that intersect at the location of the reflector.
The electrostatic actuator includes the first member and a second member which are separated by a short distance. The second member is configured to include a number of flexures that are attached to supports on the first member. The flexures allow the second member to be displaced laterally, i.e., to be a translator that moves in the direction parallel to the upper surface of the first member.
The reflector is attached to the upper surface of the first member in a manner to allow the reflector to be pivoted between the non-reflective orientation and the reflective orientation. In addition, the reflector is mechanically attached to the second member. The mechanical connection of the reflector and the second member permits the reflector to be pivoted when the second member is laterally displaced. In one embodiment, the reflector is a micromirror that resides within an interior region of the second member.
The opposing surfaces of the first and second members include electrodes that generate electrostatic forces to laterally displace the second member. The electrodes are thin strips of conductive materials that are aligned in a parallel fashion. These electrodes are positioned such that the lengths of the electrodes are perpendicular to the travel direction of the first member.
The drive electrodes are electrically coupled to one or more voltage sources that are used to provide an adjustable pattern of voltages to at least one set of drive electrodes in order to change the electrostatic forces that are generated between the sets of drive electrodes. As an example, the first set of drive electrodes may be electrically connected to a voltage source that provides a fixed pattern of voltages to the electrodes. In this example, the second set of drive electrodes may be electrically connected to a microcontroller that contains a voltage source. The microcontroller operates to provide voltages to the second set of drive electrodes in a predetermined voltage pattern. However, the microcontroller is able to reconfigure the voltage pattern by selectively applying different voltages to some of the drive electrodes of the first set. The reconfiguration of the voltage pattern modifies the electrostatic forces between the first and second members, thereby laterally displacing the second member.
In one embodiment of the optical switch, the second member (translator) includes an opening located near the center of the second member. The opening is of sufficient size to allow the reflector (micromirror) to be positioned within the opening. As the second member is laterally displaced relative to the first member (stator), the reflector pivots out of the opening to the reflective orientation. In a second embodiment of the optical switch, the reflector is located in front of the second member. In both embodiments, the reflector is attached to the second member by two actuation arms that pivot the reflector when the second member is laterally displaced.
An advantage of the invention is that the design of the electrostatic actuator and the reflector allows the optical switch to be manufactured as a micromachine. In addition, the electrostatic actuator has a low operating voltage such that the electrostatic actuator is compatible with complementary metal-oxide semiconductor (CMOS) circuitry.